Aluminium alloy sheet product with improved surface aspect

ABSTRACT

The invention relates to a rolled aluminum-based alloy product for cosmetic packaging comprising, (in weight %): Mn 1.0-1.5, Mg 0.2-0.6, Si 0.2-0.6, Fe 0.1-0.7, Cu 0.05-0.3, Cr 0-0.1, Zn 0-0.3, Ti 0-0.15, other elements ≤0.05 each and ≤0.15 total, remainder Al, wherein the fraction of Al(Fe,Mn)Si phase is at least 50%. The invention also related to a process for the manufacture of a rolled aluminum-based alloy product comprising the steps of: a) casting an ingot with a composition according to the invention; b) homogenizing the ingot at a temperature of at least 480° C.; c) hot rolling said homogenized ingot to a hot-rolled intermediate product; d) cold rolling said hot-rolled intermediate product to a cold-rolled intermediate product; e) recrystallization annealing of the cold-rolled intermediate product; f) cold rolling the annealed cold-rolled intermediate product to a cold-rolled product at final thickness; g) recovery annealing the cold-rolled product at final thickness. The products of the invention are particularly useful for cosmetic packaging, preferably for containers such as bottles, cups, tubes, holders, with a matt surface aspect.

FIELD OF THE INVENTION

The present invention relates generally to aluminium base alloys and more particularly, Al—Mn aluminium base alloys, in particular for sheet products used in cosmetic packaging.

DESCRIPTION OF RELATED ART

The surface aspect on decorative parts for cosmetic applications is of upmost importance as it plays a decisive argument for selling. Aluminium is, in this perspective, a material of first choice for high quality packaging due to its excellent formability and the possibility to create a wide range of surface aspects by applying adapted surface treatments such as etching and anodizing. These surface finishes range from bright towards matt and in combination with anodization it opens possibilities for colouring such as for example creating a gold shiny look. Many customers demand matt, and semi-matt or satin surface finish with different shades of “mattness”. This can be obtained by combination of chemical or electro-chemical polishing and etching before anodizing.

The microstructural requirements to obtain uniformly bright-anodized or matt-anodized surfaces are discussed for example in the article from R. Akeret, H. Bichsel, E. Schwall, E. Simon and M. Textor, The International Journal of Surface Engineering and Coatings, Volume 68, 1990, entitled “The Influence of chemical composition and fabrication procedures on the properties of anodized aluminium surfaces”.

Alkaline (e.g. caustic soda) etching is the most common and important pretreatment stage for anodized aluminium sheet and extrusions, particularly in architectural and decorative applications. The aim is to produce a finely etched surface with a satin-matt visual aspect as a result of the high proportion of diffuse light reflectance. Various surface aspects may be obtained as a function of metal composition, anodizing pretreatment and anodizing process.

The patent FR 2,041,635 describes a process for coloring aluminium bright or matt surfaces.

The patent application US 2014/0341678 discloses an aluminum alloy strip with improved surface appearance and a method for producing the same.

3XXX aluminum alloys are known for their formability and they are widely used in the packaging industry. Recently, these alloys have also been proposed in the automotive industry. These application do not require an anodizing layer or a specific surface aspect.

The patent application US 2015/368771 discloses an aluminium alloy having the following contents in percent by weight: Fe≤0.80%, Si≤0.50%, 0.90% Mn≤1.50%, Mg≤0.25%, Cu≤0.125%, Cr≤0.05%, Ti≤0.05%, V≤0.05%, Zr≤0.05%, the remainder being aluminium, unavoidable impurity elements, individually <0.05%, in total <0.15%, and the combined content of Mg and Cu satisfies the following relation in percent by weight: 0.15%≤Mg+Cu≤0.25%, wherein the Mg content of the aluminium alloy is greater than the Cu content of the aluminium alloy.

The patent application CN 108118201 discloses a 3005 aluminum alloy base material for a trimming plate of sedan body pillars. The aluminum alloy base material comprises the following chemical ingredient by mass percentage: 0.05-0.20% of Si, 0.40-0.60% of Fe, 0.05-0.10% of Cu, 1.00-1.30% of Mn, 0.20-0.50% of Mg, 0.05% of Cr, 0.05% of Zn, 0.004% of Na, 0.05-0.15% of other impurities and the balance of Al.

The U.S. Pat. No. 5,104,743 discloses an aluminum alloy substrate for a lithographic printing plate consisting essentially of an aluminum alloy plate containing 0.2 to 0.5% by weight of Si, 0.3 to 0.7% by weight of Fe, 0.004 to 0.02% by weight of Cu, 0.9 to 1.5% by weight of Mn, 0.05 to 0.3% by weight of Mg and 0.01 to 0.04% by weight of Ti and the balance of Al and impurities, in which the surface of said aluminum alloy plate is roughened electrolytically and anodized.

A problem that the present invention addresses is to prepare aluminum rolled products for cosmetic packaging having suitable formability and strength for these applications and responding to surface treatment such as alkaline etching and anodizing by the formation of a homogenous matt surface aspect, free of surface defects such as looper lines or anodizing bands.

SUMMARY OF THE INVENTION

An object of the invention was to provide a rolled aluminum-based alloy product for cosmetic packaging comprising, in weight %:

Mn 1.0- 1.5,

Mg 0.2-0.6,

Si 0.2-0.6,

Fe 0.1-0.7,

Cu 0.05-0.3,

Cr 0-0.1,

Zn 0-0.3,

Ti 0-0.15,

other elements ≤0.05 each and ≤0.15 total, remainder Al,

wherein the fraction of Al(Fe,Mn)Si phase is at least 50%.

Another object of the invention is a process for the manufacture of a rolled aluminum-based alloy product according to the invention comprising the steps of:

a) casting an ingot with a composition according to the invention;

b) homogenizing the ingot at a temperature of at least 480° C.;

c) hot rolling said homogenized ingot to a hot-rolled intermediate product;

d) cold rolling said hot-rolled intermediate product to a cold-rolled intermediate product;

e) recrystallization annealing of the cold-rolled intermediate product;

f) cold rolling the annealed cold-rolled intermediate product to a cold-rolled product at final thickness;

g) recovery annealing the cold-rolled product at final thickness.

Yet another object of the invention is the use of a rolled product according to the invention for cosmetic packaging, preferably for containers such as bottles, cups, tubes, holders, with a matt surface aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the microstructure of the products of example 1 in the L-LT plane. 1 a: example A-1, 1 b: example A-2, 1 c: example B-1.

FIG. 2 shows the microstructure of the products of example 1 in the L-ST plane. 2 a: example A-1, 2 b: example A-2, 2 c: example B-1.

FIG. 3 shows the intermetallics size distribution 3 a: example A-1, 3 b: example B-1.

FIG. 4 shows the scale of surface quality used for the surface evaluation.

DETAILED DESCRIPTION

Unless otherwise indicated, all the indications relating to the chemical composition of the alloys are expressed as a mass percentage by weight based on the total weight of the alloy.

In the expression Fe/Si, Fe means the Fe content in weight % and Si means the Si content in weight %. Alloy designation is in accordance with the regulations of The Aluminium Association, known to those skilled in the art. The definitions of tempers are laid down in EN 515 (1993).

Unless mentioned otherwise, static mechanical characteristics, i.e., the ultimate tensile strength UTS, the tensile yield stress TYS and the elongation at fracture E, are determined by a tensile test according to standard NF EN ISO 6892-1 (2016), the location at which the pieces are taken and their direction being defined in standard EN 485 (2016). Earing is measured according to standard EN 1669.

Unless otherwise specified, the definitions of standard EN 12258 apply.

The alloy of the invention has a specific composition which, in particular when combined with an appropriately manufacturing process, makes it possible to obtain products for cosmetic packaging having after surface treatment a homogenous matt surface aspect, free of surface defects and having simultaneously high formability and strength properties. The surface treatment typically comprises an alkaline etching step and an anodizing step.

A minimum Mn content of 1.0 and preferably 1.05 is needed to obtain sufficient strength. However the Mn content should not exceed 1.5, preferably 1.4, more preferably 1.3 to obtain the sought balance of properties, in particular homogeneous matt surface aspect after surface treatment, strength and formability.

A minimum Mg content of 0.2 and preferably 0.25 or even 0.30 is needed to obtain sufficient strength. However the Mg content should not exceed 0.6 and preferably 0.60 or even preferably 0.55 to obtain the sought balance of properties in particular homogeneous matt surface aspect after surface treatment, strength and formability.

A minimum Si content of 0.2 and preferably 0.20 or even 0.22 is needed to obtain a homogenous matt surface aspect after surface treatment. However, the Si content should not exceed 0.6 and preferably 0.5 or even preferably 0.4 or even more preferably 0.35 to obtain the sought balance of properties in particular homogeneous surface aspect, strength and formability.

A minimum Fe content of 0.1 and preferably 0.2 or even 0.30 is needed to obtain a homogenous matt surface aspect after anodizing. However, the Fe content should not exceed 0.7 and preferably 0.65 or even preferably 0.60 to obtain the sought balance of properties in particular homogeneous matt surface aspect after surface treatment, strength and formability.

The iron to silicon weight ratio Fe/Si should preferably be less than 2 and more preferably be less than 1.95 or even more preferably less than 1.9.

During casting Al(Fe,Mn) intermetallic particles are mostly formed but during processing, phase transformation from the ternary Al(Fe,Mn) phase to the quaternary Al(Fe,Mn)Si phase occurs. The present inventors have found that surprisingly it is preferably favorable for the homogeneity of the matt surface aspect that the fraction of Al(Fe,Mn)Si phase is at least 50%, preferably at least 55%, more preferably at least 60% and even more preferably at least 65%. The fraction of Al(Fe,Mn)Si phase is defined as the total 2D surface of all identified quaternary particles in a sample, divided by the total 2D surface of all detected particles and is measured by scanning electron microscopy as explained in the example. The desired fraction of Al(Fe,Mn)Si results from the combination of the product composition, particularly the Fe and Si content, with the manufacturing process. Preferably the surface fraction of Al(Fe,Mn) is less than 1.5%, preferentially less than 1%, the surface fraction of Al(Fe,Mn), being obtained from the ratio of the surface of Al(Fe,Mn) particles to the total analyzed surface. For the measurements of particles surface fractions, all particles having an equivalent diameter of larger than 0.61 μm are considered.

The Cu content should not exceed 0.3 and preferably it should not exceed 0.2. A minimum Cu content of 0.05, preferably of 0.08, more preferably 0.09 and even more preferably of 0.10 is used to obtain good chemical response to surface treatment.

Ti, usually associated with either boron or carbon can be added up to 0.15 if desired during casting in order to limit the as-cast grain size. The present invention may typically accommodate up to about 0.06 or up to about 0.05 Ti. In a preferred embodiment of the invention, the Ti content is at least about 0.01 and preferably at least about 0.02.

Chromium is preferentially avoided and is kept below 0.1, preferentially below about 0.04 and more preferentially below about 0.03.

Zinc is preferentially avoided and is kept below 0.3, preferably below 0.1, preferentially below about 0.04 and more preferentially below about 0.03.

Other elements are impurities which should have a maximum content of 0.05 wt. % each and ≤0.15 wt. % total, preferably a maximum content of 0.03 wt. % each and ≤0.10 wt. % total. The balance is aluminum.

A suitable process for producing rolled products according to the present invention comprises: (a) casting an ingot made in an alloy according to the invention, (b) homogenizing the ingot at a temperature of at least 480° C. (c) hot rolling said homogenized ingot to a hot-rolled intermediate product; (d) cold rolling said hot-rolled intermediate product to a cold-rolled intermediate product; (e) recrystallization annealing of the cold-rolled intermediate product; (f) cold rolling the annealed cold-rolled intermediate product to a cold rolled product at final thickness; (g) recovery annealing the cold-rolled product at final thickness.

The present inventors found that the combination of the composition and the manufacturing steps are particularly favorable to obtain a homogeneous matt surface. Preferably the homogenization temperature is at least 520° C., more preferentially at least 550° C. or even at least 605° C. In a preferred embodiment the homogenization temperature is at least 610° C., more preferentially at least 615° C. or even at least 618° C. The homogenization may be carried in one or several steps. The homogenization time should be preferably of at least one hour at the highest temperature, preferentially at least 5 hours and even more preferentially at least 10 hours. It is not necessary to continue the homogenization more than 30 hours.

The hot rolling entry temperature of said homogenized ingot is preferentially at least 400° C. and preferentially at least 450° C. The hot rolling exit temperature may affect the final microstructure and it is preferably at least 350° C. and preferentially at least 380° C. The hot-rolling exit thickness is preferably between 5 and 10 mm.

Cold rolling of said hot-rolled intermediate product to a cold-rolled intermediate product is then carried out, typically to a thickness between 0.6 and 2 mm preferably between 0.8 and 1.5 mm.

A recrystallization annealing of the cold-rolled intermediate product is then carried out. The temperature of the recrystallization annealing should be sufficient to ensure full recrystallization of the cold-rolled intermediate product. The temperature of the recrystallization is typically at least 300° C. or at least 320° C. The temperature should usually not be above 380° C., however conditions may differ if the recrystallization annealing is carried in a batch furnace or in a continuous annealing line.

The annealed cold-rolled intermediate product is then cold-rolled to its final thickness, which is typically between 0.2 and 1 mm, preferably between 0.4 and 0.8 mm.

A recovery annealing of the cold-rolled product at final thickness is finally carried out in order to obtain the required balance between strength and formability. The temperature of the recovery annealing or partial annealing is selected so that strength is reduced to the desired level. Typically, the recovery annealing temperature is between 200° C. and 350° C. or preferentially between 240° C. and 300° C., however conditions may differ if the recrystallization annealing is carried in a batch furnace or in a continuous annealing line. For recrystallization and recovery annealing a batch furnace is usually preferred.

The rolled product of the invention has a fine grain microstructure with a grain size in the longitudinal (L) and longitudinal transverse (LT) directions of less than 75 μm and preferably less than 65 μm with an aspect ratio less than 2.0 and preferably less than 1.8. Grain size is measured according the intercept method according to standard ASTM E112.

The mechanical properties of the product of the invention are favorable for cosmetic packaging having a good balance between formability and strength. Preferably the tensile yield strength TYS in the LT direction is at least 155 MPa preferentially at least 160 MPa, the ultimate tensile strength UTS in the LT direction is at least 185 MPa and preferentially at least 190 MPa, the elongation A50 is at least 5% and preferentially at least 6% and the earing is less than 4.3% and preferentially less than 4.0%.

The products according to the invention respond to surface treatment such as alkaline etching and anodizing by the formation of a homogenous matt surface aspect. In particular, after alkaline etching and anodizing the products of the invention are free of surface defects such as looper lines or anodizing bands. On a scale as described in FIG. 4 and after the etching and anodizing treatment described in the following example, the surface of the products of the invention are rated 0 or 1, preferably 0.

The rolled product of the invention can be used for cosmetic packaging, typically for containers such as bottles, cups, tubes, holders, particularly with a matt surface aspect. The process to transform a rolled product of the invention to a package for cosmetics comprises

-   -   Cutting blanks from the rolled product     -   Forming the blank, typically by stamping and/or drawing and/or         ironing, and/or roll-forming and/or spinning into a container,     -   Surface treating said container, preferentially to a matt         surface, by etching and anodizing.

A preferred surface treatment comprises an alkaline etching step at a temperature of at least 50° C. and a sulfuric acid anodizing step at a temperature of at least 15° C.

These, as well as other aspects of the present invention, are explained in more detail with regard to the following illustrative and non-limiting example.

EXAMPLE

Two ingots were cast, one of a product with a composition according to the invention (A), and one reference example (B). The compositions are provided in Table 1:

TABLE 1 composition (wt. %) of a cast according to the invention and a reference cast. Alloy Si Fe Cu Mn Mg Cr Zn Ti A 0.26 0.47 0.12 1.10 0.45 <0.01 0.01 0.03 B 0.22 0.54 0.01 1.04 0.01 <0.01 <0.01  0.03

The ingots were then scalped and homogenized at 620° C. for 17 hours. The ingots were hot rolled to a thickness of about 7 mm. Hot rolling entry temperature was higher than 450° C. and hot rolling exit temperature was higher than 390° C. The hot rolled products were further cold rolled to a thickness of 1 mm. An intermediate recrystallization annealing was then carried out at 340° C. The intermediate annealed recrystallized products were cold rolled again to a final thickness of 0.5 mm or 0.6 mm. A final recovery annealing was carried out in a batch furnace at 250° C. for alloy A and 285° C. for alloy B. The samples were mechanically tested, in LT direction to determine their static mechanical properties. Tensile yield strength, ultimate strength and elongation at fracture are provided in Table 2. Earing was also characterized according to EN 1669.

TABLE 2 Static mechanical properties and Earing of the samples Thickness TYS UTS Ag A50 Sheet [mm] (MPa) (MPa) [%] [%] Earing A-1 0.6 163 196 5.2 7.6 3.8 A-2 0.5 164 197 5.2 7.0 3.1 B-1 0.5 147 154 — 5.0 4.2

15

The microstructure of the finished sheets made were characterized by optical microscopy after anodic oxidation, on surface and (L-LT plane) and cross-section (L-ST section). The results are presented in FIGS. 1 and 2.

For alloy A at a thickness of 0.5 and 0.6 mm, the average grain size, measured according the intercept method according to standard ASTM E112, was 52 μm in the L direction and 34 μm in the LT direction and 54 μm in the L direction and 46 in the TL direction respectively.

For alloy B at a thickness of 0.5 mm, the average grain size, measured according the intercept method according to standard ASTM E112, was 235 μm in the L direction and 74 μm in the LT direction, with an aspect ratio in the L-LT plane of 3.2.

An overview of the average grain sizes and aspect ratio is presented in Table 3.

TABLE 3 average grain size and aspect ratio for alloy A and alloy B Thickness Grain size in L Grain size in LT aspect Sheet [μm] direction [μm] direction [μm] ratio A-1 0.5  52 34 1.5 A-2 0.6  54 46 1.2 B-1 0.5 235 74 3.2

The microstructure was further characterized by scanning electron microscopy in order to quantify the phase transformation fraction of intermetallic phases from the ternary Al(Fe,Mn) phase towards the quaternary Al(Fe,Mn)Si phase. For the quantification, several individual micrographs in a size of 250 μm×187 μm each, and with a total analyzed area of 0.92 mm² were analyzed and the ternary and quaternary particles distinguished by their different grey level in the backscattered electron contrast detection mode. The phase selection by the grey level has been done using the Bruker-Esprit 1.9 software. The observation plane lies parallel to the L-LT plane. In the used magnification, all particles having an equivalent diameter of larger than 0.61 μm have been detected and considered for the measurements leading to a total surface of detected particles of more than 25000 μm² per sample. Particle size distribution can be plotted for each material and for the two phases (See FIGS. 3a-3b ). The quantitative results are provided in in Table 4.

TABLE 4 Intermetallic phase characterization Total Surface Surface Fraction Total Total Particle of Al of Al of Al analysed particle surface (Fe, Mn) (Fe, Mn) (Fe, Mn) surface surface fraction particles Si particles Si particles [μm²] [μm²] [%] [μm²] [μm²] [%] A-1 928508 25538 2.75  7897 17640 69.1 B-1 928509 38602 4.16 21662 16941 43.9

The fraction of Al(Fe,Mn)Si phase which is defined as the 2D surface of all identified quaternary particles in a sample (Surface of Al(Fe,Mn)Si particles in Table 4), divided by the total 2D surface of all detected particles (Total particle surface in Table 4) was 69.1% for A-1 and 43.9% for B-1. The surface fraction of Al(Fe,Mn), which is obtained from the ratio of the surface of Al(Fe,Mn) particles to the total analyzed surface was 0.85% for A-1 and 2.33% for B-1.

The surface aspect on the as fabricated band material after alkaline etching removing an average thickness of 20 μm and providing a matt surface and sulfuric anodizing with an anodic layer thickness of 15 μm was tested. The detailed treatment conditions were as follows:

Etching:

-   -   alkaline degreasing at 60° C., using Bonderite C-AK708 15 g/l     -   rinsing with de-ionized water     -   alkaline etching at 50° C., using Bonderite C-ADetch1 50 g/l,         etching depth 20 μm     -   rinsing with de-ionized water     -   desmutting at room temperature, using HNO3, 50% vol.     -   rinsing with de-ionized water

Anodizing:

-   -   sulfuric anodizing at 20° C., using sulphuric acid, 200 g/l,         current density 1.5 A/dm², thickness of anodizing layer 15 μm     -   rinsing with de-ionized water.

A visual evaluation of the presence of anodizing bands was carried out with a scale defined as follows

-   0: No bands visible -   1: Fine bands visible but still homogeneous background -   2: Fine bands visible but coarser background -   3: Coarser bands with still coarser background -   4: Strong pronounced bands, background evaluation not possible

Examples of surfaces showing the different levels of anodizing bands are presented in FIG. 4.

The sheets according to the invention were rated 0, the reference sheets were rated 2-3.

The surface roughness of the rolled product of the invention was measured by profilometry. The results are presented in Table 5.

TABLE 5 Measured surface roughness Measuring Ra [μm] Rz [μm] method A-1 0.22 ± 0.0212 1.81 ± 0.183 mechanical 

1. A rolled aluminum-based alloy product for cosmetic packaging comprising, in weight %: Mn 1.0-1.5, Mg 0.2-0.6, Si 0.2-0.6, Fe 0.1-0.7, Cu 0.05-0.3, Cr 0-0.1, Zn 0-0.3, Ti 0-0.15, other elements ≤0.05 each and ≤0.15 total, remainder Al,
 2. A rolled product according to claim 1 wherein the fraction of Al(Fe,Mn)Si phase, defined as the total 2D surface of all identified quaternary particles divided by the total 2D surface of all detected particles, is at least 50%.
 3. A rolled product according to claim 1 wherein the Si content, in weight % is optionally at least 0.20 or optionally 0.22 and/or the Si content does not exceed 0.5 or optionally 0.4 or optionally 0.35.
 4. A rolled product according to claim 1 wherein the iron to silicon weight ratio is less than 2, optionally less than 1.95 or optionally less than 1.9.
 5. A rolled product according to claim 1 wherein the Ti content in weight % is at least about 0.01 and optionally at least about 0.02 and/or up to 0.06 or optionally up to 0.05.
 6. A rolled product according to claim 1 wherein, in weight %, the Cr content is less than 0.04 and/or the Zn content is less than 0.04.
 7. A rolled product according to claim 1 wherein the grain size in the L and LT directions is less than 75 μm and optionally less than 65 μm with an aspect ratio less than 2.0 and optionally less than 1.8.
 8. A rolled product according to claim 1 wherein the tensile yield strength in the LT direction is at least 155 MPa optionally at least 160 MPa, the ultimate tensile strength in the LT direction is at least 185 MPa and optionally at least 190 MPa, the elongation A50 is at least 5% and optionally at least 6% and the earing is less than 4.3 and optionally less than 4.0.
 9. A rolled product according to claim 1 wherein after etching and anodizing treatment, the surface of the product is rated 0 or
 1. 10. A process for manufacture of a rolled aluminum-based alloy product claim 1 comprising: a) casting an ingot comprising, (in weight-%) Mn 1.0-1.5, Mg 0.2-0.6, Si 0.2-0.6, Fe 0.1-0.7, Cu 0.05-0.3, Cr 0-0.1, Zn 0-0.3, Ti 0.01-0.15, other elements ≤0.05 each and ≤0.15 total, remainder Al, b) homogenizing the ingot at a temperature of at least 480° C.; c) hot rolling said homogenized ingot to a hot-rolled intermediate product; d) cold rolling said hot-rolled intermediate product to a cold-rolled intermediate product; e) recrystallization annealing of the cold-rolled intermediate product; f) cold rolling the annealed cold-rolled intermediate product to a cold-rolled product at final thickness; g) recovery annealing the cold-rolled product at final thickness.
 11. A process according to claim 10 wherein the homogenizing temperature is at least 520° C., optionally at least 550° C. and optionally at least 605° C.
 12. A process according to claim 10 wherein the hot rolling entry temperature of said homogenized ingot is at least 400° C. and optionally at least 450° C. and/or the hot rolling exit temperature is at least 350° C. and optionally at least 380° C.
 13. A process according to claim 8 wherein the cold-rolled intermediate product has a thickness between 0.6 mm and 2 mm and/or the final thickness of the cold-rolled product is between 0.2 and 1 mm.
 14. A product comprising a rolled product according claim 1 for cosmetic packaging, preferably optionally for one or more containers optionally one or more of bottles, cups, tubes, holders, with a matt surface aspect.
 15. The product according to claim 14 wherein a process to transform the rolled product to a package for cosmetics comprises cutting one or more blanks from the rolled product forming the blank, optionally typically by stamping and/or drawing and/or ironing, and/or roll-forming and/or spinning into a container, surface treating said container, optionally to a matt surface, by etching and anodizing.
 16. The product according to claim 14 wherein the surface treating comprises an alkaline etching at a temperature of at least 50° C. and a sulfuric acid anodizing step at a temperature of at least 15° C. 